HeLa (S) and Chinese hamster ovary (CHO) cells respond to biomedical ultrasound (1.1 MHz, 0.5 to 20 W/cm2) by lysis, reduced viability, and an increased frequency of giant cells. The amount of lysis and reduction in cell viability are intensity dependent, with an initial threshold occurring at approximate intensity of 1 W/cm2. Future research includes analyses on cell doubling times, cell cycle component (G1, S, G2, and M) durations and ratios, and chromosomal structure and function through macromolecular hybridization. The present information and results suggests that biomedical ultrasound does perturb mammalian in vitro cell systems.